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The performance of SQL query statements affects the performance of the entire database to a certain extent. In many cases, poor database performance is almost caused by poor SQL statements. SQL statement executionThe Plan determines how the SQL statement extracts data from the database and returns the data to the client. This document describes how to obtain the SQL statement execution plan through the explain Plan.The execution plan of the SQL statem

In-depth analysis of explain for MySQL Query optimization MySQLexplain BitsCN.com When analyzing query performance, it is also useful to consider the EXPLAIN keyword. The EXPLAIN keyword is generally placed before the SELECT query statement to describe how MySQL performs the query operation, and the number of rows to be executed in the result set returned by MySQ

Usually when optimizing SQL queries, we use explain to analyze SQL execution plans, usually when we use a composite index, how do we judge the index to be fully used? Of course, the master look at the table structure and SQL statements to know exactly how many fields to use, for unfamiliar students. We can still look at the length of the Key_len, of course, this calculation is still a bit complicated, but after you read my blog, I believe you will cer

Tags: Test not DEP info SSI Pass Cache Execute andUsage: Explain SQLRole: For parsing SQL statementsMysql> Explain select * from quser_1 where loginemail = "[email protected]", +----+-------------+---------+------+---- -------------+-----------------+---------+-------+------+-----------------------+| ID | Select_type | Table | type | Possible_keys | key | key_len | ref | rows | Extra

Turn from: http://blog.csdn.net/zhuxineli/article/details/14455029 (simple study and turn)Explain shows how MySQL uses indexes to process SELECT statements and join tables. Can help select better indexes and write more optimized query statements.Parse an SQL statement first to see what appearsEXPLAINSELECTs.UID,s.username,s.name,F.Email,F.Mobile,F.Phone,F.PostalCode,F.Address from Uchome_space ass,Uchome_spacefield asFWHERE 1 and s.GroupID=0 and s.U

MySQL performance analysis and explain usage knowledge is the main content of this article, and then let us through some practical examples to introduce the process, I hope to be able to help you.1. Use the Explain statement to view the results of the analysissuch as explain select * from Test1 where id=1; appears: ID selecttype table type possible_keys key Key_l

Tags: mysqlThe Type field in the explain execution plan is divided into the following types: All INDEX RANGE REF eq_ref const,system NULLFrom left to right, performance from worst to bestType = all, full table scan, MySQL scan full table to find matching rows (because rating is not an index in the film table) mysql> explain extended select * from film where rating > 9\g 1. Row *************************** id

Explain syntax Hive provides the explain command to display the query execution plan. Syntax: Explain [extended] Query The explain statement uses extended to provide additional information about the operation in the execution plan. This is a typical physical information, such as a file name. Hive queries are co

than half of the results in the set are returned, the full table scan is more efficient than the query index. Creating too many indexes will lead to a very slow insertion and will also occupy a lot of space. You can use the explain and hint tools for analysis. If the index has a direction, the reverse order is still ascending. The default maximum number of indexes for each set is 64. 1. View Indexes > db.jiunile_events.getIndexes();[ {

Tags: div must optimize ext MySQL Optimization order index instead of MySQL optimizationThe explain command is the first recommended command to address database performance, and most performance issues can be easily resolved with this command, explain can be used to see how SQL statements are executed, to help select better indexes and refine query statements, and to write better optimization statements.

automatically indexed, so the query is fairly fast. You can read more about its content on the 10gen website. Index all queriesWhen I first used MONGO, I sometimes executed queries on a specific underlying environment or from a scheduled task. Initially those queries were not indexed because there was no need to face the user or to run frequently. This, however, poses a performance problem for other index queries because queries that are not indexed do a lot of disk reads, which affects the re

Tag: Represents the + + table operation retrieval distinct additional buffer 2.4 throughExplain is primarily used to obtain a query execution plan that describes how MySQL performs query operations, the order of execution, the indexes used, and the number of rows that MySQL will need to execute to successfully return a result set. can help us to analyze the SELECT statement, let us know why the query is inefficient, so as to improve our query, so that the query optimizer can work better.Explain

Explanation of explain functions in Mysql and mysqlexplain I. MYSQL Indexes Index: a data structure that helps Mysql efficiently obtain data. To improve search efficiency, you can compare it to a dictionary. It can be simply understood as a sorted data structure for fast search. Index function:It is easy to query and sort (So adding an index will affect the where statement and order by sort Statement ). In addition to data, databases also maintain dat

Mysql Explain command, mysqlexplain The MySQL EXPLAIN command is used to query the Execution Plan (QEP) of an SQL statement ). The output results of this command show us how the MySQL optimizer executes SQL statements. This command does not provide any adjustment suggestions, but it can provide important information to help you make optimization decisions. For more information, see the official documentatio

The following articles mainly summarize the practical application skills of the Oracle explain plan. If you need to optimize the SQL statements in the Oracle database, we need to know the relevant plans to be executed, so as to make targeted adjustments. There are several methods to obtain the Oracle execution plan, which will be summarized below. 1. Use of EXPLAIN Every SQL statement executed by the Oracle

MySQLDatabaseEXPLAINThe usage and precautions are the main content we will introduce in this article. Next let's take a look at this part. 1. EXPLAIN tbl_name is a synonym for DESCRIBE tbl_name or show columns from tbl_name. 2. EXPLAIN [EXTENDED] SELECT select_options if the keyword EXPLAIN is put before the SELECT statement, MySQL will

When analyzing query performance, it is also useful to consider the explain keyword. The Explain keyword is typically placed in front of a SELECT query statement to describe how MySQL performs a query operation and the number of rows that MySQL needs to perform to successfully return the result set. Explain can help us analyze the SELECT statement, let us know wh

EXPLAIN commands in MySQL, mysqlexplain The explain command in MySQL shows how mysql uses indexes to process select statements and connect tables. The information displayed in the explain statement can help you select a better index and write a more optimized query statement. 1. How to Use EXPLAIN:Add the explain state

I. Syntax EXPLAIN select sid,filename,filetype from (SELECT * from by_disk_file where uid=830814) a Result: Id: indicates the SQL Execution sequence. The SQL statements are executed from large to small. Select_type: Query type, which can be: 1. SIMPLE Simple SELECT (do not use UNION or subquery) For example: explain SELECT * from by_disk_file where uid=830814 2. PRIMARY Query operations on the outermost la

Explain (1) SQL statement in mysql) Explain is used to analyze how mysql uses indexes to process select statements and connect tables. It can help you select better indexes and write more optimized query statements.1. id Statement execution sequence identifier. The execution sequence of select statements.2. select_type: 2.1, simple Simple type, as long as there is no subquery or union in the statement.